Role-Based Access Control (RBAC) is essential for secure and scalable B2B SaaS applications, as it organizes permissions into roles rather than assigning them directly to individuals, facilitating easier management across multi-tenant environments. This framework not only enforces least-privilege access but also aids in maintaining consistent permissions as teams and products evolve. RBAC is pivotal for developers, impacting onboarding, enterprise readiness, and scalability. The guide discusses leading RBAC providers such as Descope, Auth0, and Microsoft Entra, highlighting their capabilities and suitability for different needs, from tenant-aware roles to enterprise SSO integration. Descope, in particular, offers a comprehensive platform that unifies authentication and authorization, streamlining access control in multi-tenant environments. The choice of an RBAC provider should consider factors like multi-tenant role management, policy enforcement, and integration with enterprise workflows to ensure secure and efficient access control.